[roll] Roll fuchsia [flatland] Fix race for initial present

This CL fixes a race in carnelian logic for the very first present.
If we are to queue the very first present before receiving
OnNextFrameBegin(), we have 1 pending and allowed present which failed
at this check.

Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/594083
Original-Revision: 6e26a891f38a45b6e40f8694dd1949d00bc32821
GitOrigin-RevId: f42188af7815a216a80bdd83b2f0d175b196332d
Change-Id: I998d2d88676176f248ad068871dbc140d070621b
diff --git a/stem b/stem
index 46135a3..fa2d757 100644
--- a/stem
+++ b/stem
@@ -10,7 +10,7 @@
              githooks=""
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="9df7d185ab7368fb1418d5edd6006949fcc05e53"/>
+             revision="6e26a891f38a45b6e40f8694dd1949d00bc32821"/>
   </projects>
   <hooks>
     <hook name="install-environment"